This application claims a priority from German patent application 100 26 019.5, filed May 25, 2000, and the contents of that application are hereby incorporated by reference herein.
This invention concerns an inductive position sensor, particularly for use with motor vehicles, having an oscillator circuit which creates a periodic alternating voltage signal and which is coupled to an exciting coil, a plurality of receiving coils with the exciting coil and the receiving coils being structured as printed conductors or leads on a base plate or circuit board, an evaluation circuit to evaluate signals induced in the receiving coils, and a movable induction coupling element which influences a strength of inductive coupling between the exciting coil and the receiving coils.
Such a position sensor is disclosed in German patent application DE 197 38 836 A1.
A principle of this type of inductive sensor is based on inductively out-coupling of energy in the movable element that, in turn, inductively feeds back to receiving conductor loops having a special geometry. The geometry of the receiving conductor loops is chosen such that the induced voltage in the receiving conductor loops depends upon the position of the movable element.
Prior art systems and components require a significant amount of space. It is normally preferable to find solutions that require the least amount of space. This is particularly true for uses in automobiles.
An inductive sensor, however, requires a minimal surface for sensor geometry because a signal voltage of the sensor ultimately depends on coil surface area of the available coils, and the signal voltage should preferably not be small. Further, electronic circuitry also requires additional space.
It is an object of this invention to provide an inductive position sensor having a space-saving structure.
According to principles of this invention, evaluation circuitry is arranged within the geometry of the sending (exciting) and/or receiving coils and effective surfaces of the receiving coils at beginning and/or end areas of the sensor are structured such that, when no movable element is present, a zero voltage results at taps of the receiving coils.
The first part of this solution is, therefore, that the evaluation circuitry is arranged within the geometry of the sending and/or receiving coils. This results in the benefits of a reduced space requirement of the sensor structure and a reduced cost because of smaller circuit boards or base plates.
This, however, leads to an asymmetrical loading of the sensor, because pads, leads and components necessary for circuitry form partial inductive short circuits. The effect is that voltage induced in the receiving coils by the exciting coil differs from zero, so that an offset voltage appears on receiving-coil terminals. In the second part of this solution, these offset voltages are compensated for by adapting the geometry of the receiving coils at beginning or ending areas of the sensor.